there are pages and pages of this sort of stuff, feel free to browse MS for the differences.

Windows XP Professional Product Documentation
Security and administration
Windows XP is loaded with new tools and programs that ensure the privacy and security of your data, and help you operate your computer at peak performance. Learn how to assign a password, lock your computer, back up files and folders, and more to protect the contents of your computer. Discover how to manage computer components, services, and system tools; and how to work with disk management and encryption features.

What's new in Windows XP Professional
Thank you for choosing to use Windows XP professional! There are many new and exciting features at your fingertips. Some of these features are making their debut in Windows XP professional, and others have been improved upon since earlier releases of Windows. There are new tools you can use to get the most out of your computer experience, and other technologies that run in the background, making your computer run more efficiently and reliably.
First, what you can't see: Windows XP professional has great capability in the behind-the-scenes running of your computer. Overall security has been improved, making it even safer for you to shop and browse on the Internet. You can also communicate with other people on other networks without worrying about compromising your privacy or your personal data files. Performance is at an all-time high, allowing you to use more programs and have them run faster than ever. Windows XP professional is dependable and stable, so you can always rely on the performance and effectiveness of your computer. Best of all, compatibility with other programs is better than ever.
Now, what you can see: Windows XP professional has many features and tools that will make using your computer easy, effective, and entertaining. For example, you can use Remote Desktop to access your work computer and its resources from home, and to view files and documents on your computer's desktop from a co-worker's computer. With NetMeeting you can have virtual meetings with anyone, anywhere, and you can participate in discussions using audio, video, or chat. Getting help has never been easier: with Remote Assistance, you just send e-mail to your favorite computer expert or Help desk personnel and they can help you fix a problem from their location. Windows XP professional provides extensive online Help for all operating system features, as well as a digital tour to help you discover the possibilities awaiting you.

That is Beautiful.
I'm with Milen on this one. XP is a resource hog. Even when you turn off all of the crap, it's still got a lot of overhead.
I prefer WIn2k as it is extremely reliable. I have not rebooted my machine at home in 9 months. try that with XP.
The main inhancement the XP offers is the "Firewall" and that was a joke. SP2 gives a new one that works, but who is going to use it?
The only real trouble with holding onto Win2k is that the support for this OS will not last much longer. I suspect I will be moving to XP sooner or later, but by then, I will have found ways to make the OS work for me...